This invention relates to a shaft seal device for sealing a reciprocating shaft. More particularly, it relates to a type thereof, wherein working fluid is substantially prevented from leakage at the sealing area in a Stirling cycle engine.
Stirling engines have received increasing attention in recent years because their smooth torque characteristics, clean exhaust gases, low noise, low fuel expense, low maintenance, and high durability when compared with a conventional gasoline engine. Furthermore, thermal efficiency of a Stirling engine is quite excellent since it's performance is similar to Carnot's cycle in comparison with that obtained by the internal combustion engine, and moreover, since fluid having relatively small molecular structure such as hydrogen or helium is used as the working fluid in a Stirling engine, excellent temperature efficiency of the thermal heat exchangers is obtained, and hydrodynamic loss can be reduced during operation.
However, engine materials may be deteriorated (become brittle) due to the employment of hydrogen, and more importantly, sealability comes into the biggest question. That is, since hydrogen or helium as the working fluid has a relatively small molecular structure, it is difficult to properly seal a Stirling engine. Stirling engines have accordingly exhibited high leakage rates in the seal area between the cylinder wall and the piston rod. Conventional "roll sox" seals have been reasonably effective for sealing but their durability is low due to fatigue caused by large repeated movement thereof, and due to the choice of flexible materials used therein.
In the sealing means of a Stirling engine, compact sealing means for use in a compact Stirling engine has been particularly requested. Recently, multiple seal rings have been used to form a compound seal with a block seal portion and a liquid seal portion positioned therebelow in order to enhance durability.
However, the problem of leakage of the sealing liquid used in the liquid seal portion has remained, and research to solve this problem has not defined a suitable mechanism therefor. Hence, the problem of leakage remains and effective engine design must take such leakage into consideration.